This invention relates to treatment of a radioactive waste, and more particularly to a process for treating a radioactive waste, which is suitable for converting a concentrated liquid waste, particularly a concentrated liquid waste containing sodium borate as a main component, as produced from an atomic power plant based on a pressurized water reactor (PWR) to homogeneous powder.
Liquid wastes containing radioactive substances (sodium sulfate as a main component), as produced from an atomic power plant based on a boiling water reactor (BWR) have been so far dried and pulverized by a thin film evaporator to attain a large volume reduction, as disclosed in Japanese Patent Application Kokai (Laid-open) No. 54-29878, Japanese Patent Application Kokai (Laid-open) No. 61-28897, etc. Heating of the liquid wastes in the centrifugal film drier has been usually carried out by introducing superheated steam at about 170.degree. C. into a jacket provided on the outside shell surface of the thin film evaporator from a boiler in the atomic power plant.
The present inventors have tried to dry and pulverize a concentrated liquid waste containing sodium borate as a main component as produced from the PWR power plant by a thin film evaporator, and have found that in the case of the liquid waste containing sodium borate as the main component there appears a foaming phenomenon during the step of drying and pulverization and no homogeneous powder can be obtained. The power that has experienced the foaming phenomenon cannot undergo successive pelletization with good success. Furthermore, when the powder that has experienced the foaming phenomenon is solidified, no homogeneous solidified mass of radioactive waste can be obtained.